Makes the files parsable as c++ files.

Bug: chromium:943709
Change-Id: I6f7d718f9773fe4a7f72828ee9cd56beb5577c66
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1545528Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>